1. Field of the Invention
This invention relates in general to certain new and useful improvements in electrical transmission cables and, more particularly, to electrical transmission cables which have a composite reinforced component to provide loading capabilities.
2. Brief Description of the Related Art
In electrical conductors and, particularly, long distance electrical conductors, copper was frequently employed because of its superior conductive properties and was widely used until about the time of World War II, at which point its primary use was directed to war efforts. Prior to that time, and even thereafter, conductor technology and the selection and mixture of different wire materials has evolved gradually since the end of the Nineteenth Century. However, after World War II, aluminum was widely used in place of copper conductors and was soon integrated with a steel core in electrical transmission cables for greater strength. Today, the aluminum conductor, which is steel reinforced (referred to as “ACSR”), remains as an industry standard.
The evolution of conductors continued with the introduction of a compacted overhead conductor which provided greater conductivity with the same diameter as the aluminum conductor steel reinforced cable. However, in about 1985, the aluminum conductor which was steel supported, frequently referred to as “ACSS”, was introduced by Reynolds Cable and has gained wide commercial acceptance in the past few years. The ACSS cable is designed for high voltage transmission with less sag. However, the compacted overhead conductor and the ACSS cable are priced about ten percent higher than the ACSR.
The evolution of conductor technology has moved to the exploratory use of composite cores, such as carbon, ceramics and fiberglass, with the advent of research leading to the present invention. These materials offer unprecedented technical performance advantages over the earlier conductive materials. However, higher material costs and limited production has resulted in prices of up to ten times that of the ACSR conductor. Thus, the major challenge associated with these promising composite conductors is to become price competitive. It is desirable to provide a composite reinforced aluminum conductor for replacement of the heavy steel strength member of the ACSR with a high strength and lower weight glass-fiber composite material. The current carrying component is still pure aluminum. The main difference between the ACSR and the composite reinforced aluminum conductor (“CRAC”) is that the CRAC will have a higher percentage by volume of a conductive component. This improvement is actually made possible by the much greater tensile strength of the glass relative to the steel and this frees up space in the conductor's volume for more aluminum. This further significantly increases conductor current carrying capacity along with significantly lower weight.
It can be seen from the above that some of the specific advantages of the CRAC is that:
1. The cost of the composite reinforced conductor is equal or less than the cost of the traditional steel cable conductor of the same diameter.
2. The composite materials used as the center core have a coefficient of thermal expansion which is fifty percent less than the steel core reinforcement.
3. The tensile strength (breaking strength) is about one hundred fifty percent higher than carbon steel core wire (with HC steel being approximately 210 ksi).
4. Conductivity of composite reinforced conductors is at least forty percent higher and having a target value of as much as two hundred percent higher than ACSR conductors of the same is outer diameter.
5. The CRAC conductors are also capable of utilizing transmission and distribution (T&D) accessories and other accessories which are installed in a similar manner in traditional cable.
6. The CRAC cables have the capability of being used with field installation equipment and procedures which exist with minimum modifications.
7. The composite materials are compatible with conventional wire and cable process technology.
8. The CRAC cables eliminate eddy-current heating.
9. A solid aluminum core has 1/100 degree of radial temperature differences as compared to stranded wire.
10. There is no loss of strength in a CRAC and consequent increase in sag due to annealing of the tension member.
11. The CRAC has simplified manufacturing requirements because there is no need for multiple layers of stranded aluminum in order to cancel out self-inductance.
12. There is an elimination of non-uniform current flow due to self-inductance when using the CRAC.
In addition to the other advantages, the new CRAC conductor of the present invention has at least twice the recycling effectiveness as does the ACSR. The existence of this new CRAC along with commercial manufacturing processes allows for wire extrusion stranding and composite pultrusion processes to be used in combination in a continuous high speed, low cost, mass production assembly line. The process also converts aluminum into a high value added product by producing and integrating a lightweight composite material strength member and an optical fiber for data transmission and intelligence monitoring.